set first FAQ link to mktg webiste too

The first FAQ link in the help modal was missing a redirect to the mktg site (if there is a mktg site)

See the second FAQ link: https://github.com/edx/edx-platform/blob/cb3429570c67ca6b3c5ca6c5898486975d353844/lms/templates/help_modal.html#L115

@gwprice 
@sarina